1. Mitigating Alkali Silicate Reaction using Fly Ash ACI Spring 2008 Convention Los Angeles, CA
by Dr. David L. Gress
Recycled Materials Resource Center Department of Civil Engineering University of New Hampshire

2. Acknowledgements
RMRC
FHWA

3. ASR, what is it?
Reactive Aggregates
Alkali
High pH
Calcium
ASR gel

4. ASR Background 1922 - Buck Hydroelectric Plant (New River, Virginia)
ASR distress within 10 years
Thomas E. Stanton
1938, PCC Failure (California)
1st Published Article on ASR (ASCE)

5. ASR Gel Forms in concrete pore system Swells with water absorption
Tensile stresses cause concrete to fail

7. Materials and Mitigation Strategies
Low Alkali Cement ( 0.3 Na2Oeq)
Class F Fly Ash (15 to 25% Substitution)
Ground Granulated Blast Furnace Slag (GGBFS) (25 to 55% Substitution)
Lithium Nitrate (70 to 150% Dosage)
Silica Fume Blended Cement (7 to 12% Substitution)
Metakaolin (10 % Substitution)
Class C Fly Ash (>>35%)

8. Class F Fly Ash Burning Pulverized Bituminous Coal Low Calcium Content
Pozzolan + H2O + Ca(OH)2 = CSH
Consumes Calcium
Ties up Alkali in CSH
pH lowers and ASR stops
Supplements the Portland Cement
Improved Density and Permeability

9. Class C Fly Ash Burning Pulverized Sub-bituminous Coal
High Calcium Content
Higher Alkali content
Higher Alkali Solubility
Requires Higher Dose to be Effective
Pozzolan + H2O + Ca(OH)2 = CSH
Ties up Alkali but also contributes Alkali and Calcium
Supplements the Portland Cement
Improved Density and Permeability

10. Accepted Testing Procedures
ASTM C1260 (Mortar –Bar Method)
ASTM C1293 (Standard Prism Beam)

11. ASTM C 1260 1 x 1 x 11” samples Submerged in 1N NaOH 80° C (176° F)
14-day test duration
> 0.10 % expansion shows potentially ASR reactive aggregate

12. ASTM C 1293 3 x 3 x 11” samples Over water 38° C (100° F) 100% RH
1 to 2 year test duration
> 0.04 % expansion shows potentially ASR reactive concrete

13. Effect of Fly Ash and Slag on Alkali-Silica Reactivity
Fig Effect of different fly ashes and slag on alkali-silica reactivity. Note that some ashes are more effective than others in controlling the reaction and that dosage of the ash or slag is critical. A highly reactive natural aggregate was used in this test. A less reactive aggregate would require less ash or slag to control the reaction. A common limit for evaluating the effectiveness of pozzolans or slags is 0.10% expansion using this rapid mortar bar test (Detwiler 2002).

15. Colorado Springs Airport

16. Colorado Springs Airport

17. Colorado Springs Airport

18. Tri Services (Navy, Air Force, Army)
DOD Guide Specifications for airfields
32 DOD airports have ASR
Class F Fly Ash only

19. Mitigation of Alkali-Silica Reactivity in New Mexico R
Mitigation of Alkali-Silica Reactivity in New Mexico R. Gordon McKeen, P.E. etal

20. > 35 % Class C required

21. > 40 % Class C required